The dependencies of the integral cross sections for the title reactions on collision energies were determined from 0.6 kcal/mol to nearly 6 kcal/mol. The result provides, for the first time, direct and unambiguous experimental evidence for the existence of an abstraction pathway, in addition to the widely accepted inserted one. A reaction barrier of about 1.8 kcal/mol was found for this elusive abstraction channel. The branching of these two microscopic pathways was estimated. An intriguing H/D isotope effect was revealed, which called for further studies.